1. Exercism.IO

Exercism.io is a growing platform designed to help people increase their javaScript and other coding skills with test and challenges. the program offers challenges for 51 langauges and is entirely free-of-charge. As of now, over 50,000 students used the javaScript challenges offered by exercism.io.

2. topcoder.com

If you want a time-tested javaScript coding challenges site, look no further than TopCoder. This coding challenges every week. What's more, it has a vast archive of challenges in which you can play to your heart's delight. It have vast community where you can learn and grow connect with different people. Also you can Earn $$ via gig work and challenges.

3. codewars.com

Codewars offers a variety of javascript challenges designed to test different area of expertise, including combined with other programming language. The simplest project available is called "Polish Alphabet" and is Javascript-only. Codewars challenges you to change a group of letters into a word using diactritics.